Process for preparation of chemically stable, dry-flow, low compact, dust free, soluble granules of phosphoroamidothioates

ABSTRACT

Dry flow, low compact, dust free, soluble granules of phosphoroamidothioates, preferably acephate, are produced by the process of 1) pre-mixing technical grade phosphoroamidothioate with specified adjuvants and other inert ingredients; 2) grinding to produce a ground product having a preferred particle size of 5 microns to 10 microns; 3) post-mixing; 4) granulating; 5) drying; 6) sizing to required length, preferably 1.5 to 3.0 mm; 7) and sieving to remove the fines to get the desired dust free soluble granule.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit, under 35 U.S.C. 119(e), ofU.S. Provisional Application No. 60/340,272 filed Dec. 18, 2001, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a process for preparinginsecticidally active soluble granules of phosphoroamidothioate,referred to herein as acephate.

[0004] 2. Background Information

[0005] In recent years, agricultural chemicals have been most preferablyformulated in the form of dusts, wettable powders, soluble powders,emulsifiable concentrates, soluble liquid/concentrates, granules, coatedgranules, water dispersible granules, suspension concentrates, andsolutions. Occasionally, when dusts are produced by absorbing or mixingactive ingredients with a finely divided inert carrier material, forexample China Clay or the like, drift problems occur. With wettablepowders and soluble powders the problems faced at the time of dilutionare not only drift, but the final disposal of containers, for dustparticles tend to stick to sides of the containers. The left overmaterials within the containers pose great problems to the environment,operators and users.

[0006] Although dusts are undesirable because of airborne contaminationand handling difficulties, liquid spray formulations have not providedan acceptable alternative, for they involve solvents and packagingexpenses, along with container disposal requirements that detract fromtheir commercial desirability.

[0007] Water dispersible granules produced by fluidized bed spray dryersovercome the problems associated with wettable powders and solublepowders, but have high processing costs and require high value capitalinvestment, as well as requiring highly skilled staff. These problemsimpose a significant barrier in widening the market acceptance of thesecompounds.

[0008] Certain phosphoroamidothioates and phosphoroamidodithioates,collectively referred to as Phosphoroamidothioates, are known to haveexcellent insecticidal activity against a variety of insects and in avariety of environments. Acephate, one of the important commercialinsecticides within this class of compounds, is a systemic and contactinsecticide of moderate persistence with residual activity lasting about10-15 days. It is effective against a wide range of aphids, leaf-miners,lepidopterous, larvae, sawflies and thrips and it is also anon-phytotoxic on many crop plants.

[0009] Phosphoroamidothioate containing pellets have been proposed inthe past, but difficulties have been encountered in pelletizing acephatetechnical, the preferred insecticide within the class ofphosphoroamidothioates. Attempts to manufacture acephate technicalpellets from acephate technical powders have been proposed and have beenunsuccessful.

[0010] Considerable experimentation in the area of producing thepreferred high-strength acephate granules has been conducted andconfirms the manufacturing difficulties which earlier formulators haveexperienced. Furthermore, the pellets and methods proposed for makingpellets suggested in the prior art leave considerable room forimprovement. Prior extrusion processes have proposed the addition ofcostly surfactants, the combination of phosphoroamidothioate with asecond active ingredient, or the creation of a mixture of the activeingredient with a solvent in an amount of from 3-25% by weight beforeextrusion, but these processes have not solved the problems encountered.

[0011] The formulation of acephate presently in use is acephate 75%soluble powder having acephate active ingredient 75% (w/w), surfactant 1to 2% (w/w), inert filler (precipitated silica) to make 100% (w/w).Acephate 75% soluble powder poses the problems of dust, low pourability,high transportation costs, high capital manufacturing investment,measurement difficulties, difficulties in packing material disposal,handling problems, high risk of caking and others.

[0012] Because of the problems associated with producing granular formsof phosphoroamidothioates, such as the preferred acephate, there is aneed in the art for a process for preparing chemically stable, dry flow,low compact, dust free, insecticidally active soluble granules ofphosphoroamidothioate which are useful from a practical stand point, aswell as for a low cost, practical manufacturing technique which can bepracticed on a commercial scale without requiring expensive additives orsolvents.

SUMMARY OF THE INVENTION.

[0013] By the present invention the above-identified major limitationshave been overcome. The method for producing dry flow, low-compact, dustfree, soluble phosphoroamidothioate granules, such as the preferredcompound acephate, is an improvement over prior manufacturing processes.Further, the dust free soluble granules produced by this invention,which has a concentration of the insecticidally active ingredient inthis formulation may vary from 40-98% of phosphoroamidothioate activeingredient, is more advantageous than prior granular products andexhibits certain very desirable characteristics as noted hereinafter.

[0014] Briefly, and in accordance with a preferred embodiment of theinvention, dry flow, low compact, dust free, soluble granules ofinsecticially active phosphoroamidothioate are prepared by forming apre-mix containing the required quantity of phosphoroamidothioate, adispersing agent, a wetting agent, a binding agent, an antifoamingagent, a disintegrating agent, a stabilizer and filler. The specifiedadjuvants have a maximum of 1% water insoluble matter. This pre-mix isthen ground to produce a ground product having preferred particle sizesbetween 5.0 microns to 10.0 microns. The ground product is fed to apost-mixer to form a mixture. The mixture is then fed through a hopperinto a granulator where granules are formed. The granules are thendried, and the dried granules are sized and sieved to separate drygranules from fines, producing dry flow, low compact, dust free, solublegranules of phosphoro-amidothioate as noted above, the preferredphosphoroamidothioate is acephate. The fines may be recycled back to thepost mixer.

[0015] This invention produces essentially dry flow, low compact, dustfree soluble phosphoroamidothioate granules having a preferred granulesize of 1.5 to 3.0 mm in length and 0.5 to 1.0 mm in diameter. Thesegranules of phosphoroamidothioates are characterized by aging stabilityfor a minimum of two years.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features and advantages of the present invention will becomeapparent from the following detailed description of preferredembodiments thereof, taken in conjunction with the accompanyingdrawings, in which:

[0017]FIG. 1 is a flow chart of the preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The process of the present invention is best described byreferring to the flow chart in FIG. 1. An essentially dry pre-mixcomprising about 95% to 99% of solids and 1% to 5% moisture and/orsolvent is formed from the following ingredients: 40% to 98% of theinsecticidally active compound 2, 0.1% to 5.0% dispersing agent 4, 0.1%to 3.0% wetting agent 6, 0.1% to 3.0% binding agent 8, 0.01% to 0.08%antifoaming agent 10, 0.01% to 10.0% disintegrating agent 12, 0.01% to1.0% stabilizer 14, and fillers 16 to make 100% (w/w). Theinsecticidally active compounds of the present invention have thefollowing formula:

[0019] wherein R and R¹ individually are an alkyl, alkenyl or alkynylgroup containing upto 6 carbon atoms, R² is hydrogen, an alkyl groupcontaining 1 to 18 carbon atoms, a cycloalkyl group containing 3 to 8carbon atoms, an alkenyl group containins 2 to 18 carbon atoms or analkynyl group containing 3 to 18 carbon atoms, R³ is hydrogen or analkyl group containing 1 to 6 carbon atoms, and Y is oxygen or sulfur.All of the inert ingredients are preferably solids and in a powder form.In one preferred embodiment, the binding agent 8 is selected fromsucrose and starch derivatives or a blend thereof, the wetting agent 6is selected from calcium or sodium salt of alkyl aryl sulphonate, thedispersing agent 4 is selected from the derivative of sulfonated fattyalcohols, the disintegrating agent 12 is selected from swelling typeclays such as Bentonite and zeolite, the antifoaming agent 10 isselected from silicon oil derivatives, the stabiliser 14 is selectedfrom salts of higher fatty acids, and the filler 16 is selected fromprecipitated silica and kaoline and the like. Grinding 22 of the pre-mix20 is then conducted, preferably in a microniser, to obtain a groundproduct 24 having a preferred particle size of 5 microns to 10 microns.

[0020] The ground product 24 is subjected to post-mixing 26 to form amixture 28 which is then made into granules 36 by preferably charging30, by way of a rotary feeder, a feeding hopper which supplies themixture to a granulator for granulation 34. The granulator that performsthe granulation 34 has a preferred inlet temperature between 30 to 35°C. and a preferred outlet temperature of between 40° C. to 45° C. Theresulting granules 36 are subjected to a drying 38 process, preferablyby passing the granules 36 through an air chamber, producing drygranules 40.

[0021] Sizing 42 the dry granules 40 is then accomplished to producesized granules 44 of a desired length and diameter. Sizing the granulesis preferably conducted by passing the dry granules 40 through anoscillating cutter to obtain granules which are preferably between about1.5 mm and 3.0 mm in length and 0.5 mm to 1.0 mm in diameter. Aftersizing, the sized granules 44 are subjected to sieving 46 to separatefines 50 generated during the sizing process from desired dust freesoluble granules 51.

[0022] The fines 50 from the sieving 46 process may be collected andrecycled at the charging 30 stage of the process to obtain a minimumyield of 99.0% dry flowable, low compact, dust free, soluble granules 54of phosphoroamidothioates, preferably acephate.

[0023] The dust free soluble granules 54 were tested for requiredquality specifications and packed in desired packing. This techniquegives 99% of conversion yield. The dust free soluble granules 54 enjoyall the formulation advantages described above, producing dust freesoluble granules 54 which are beneficial from an economic aspect and ahandling aspect and which show a very good performance during use.

[0024] The following examples are presented to illustrate but not torestrict the present invention. Parts and percentage are by weightunless otherwise specified.

EXAMPLE 1

[0025] Acephate 97% Granules can be prepared as follows:

[0026] Composition Ingredients Quantity (% w/w) Acephate Technical 98.5%purity 98.48 Dispersing agent 0.50 Wetting agent 0.10 Binding agent 0.10Antifoaming agent 0.03 Disintegrating agent 0.50 Stabilizer 0.05 Filler0.24 Total 100.00

Example 1 Process

[0027] The constituents of the above composition are mixed in apre-mixer, then ground in a microniser to the required size of 5 micronto 10 micron. The ground product 24 is again mixed in a post-mixer toget a uniform homogeneous mixture 28. This homogeneous mixture 28 isthen fed through a rotary feeder into a low compaction granulator, whilemaintaining an inlet temperature of 32 to 35° C. and an outlettemperature of 40 to 45° C. The Acephate granules 36 formed in thegranulator are further dried through an air chamber, sized to 1.5 mm to3 mm length, and are collected. The fines 50 generated during theprocess are recharged to get a conversion yield of 99 percent.

Example 2

[0028] Acephate 98% granules can be prepared as follows:

[0029] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 99.50 Dispersing agent 0.25 Wetting agent 0.03 Binding agent 0.05Antifoaming agent 0.02 Disintegrating agent 0.05 Stabilizer 0.05 Filler0.05 Total 100.00

[0030] Acephate 98% granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

Example 3

[0031] Acephate 97.5% granules can be prepared as follows:

[0032] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 98.99 Dispersing agent 0.40 Wetting agent 0.10 Binding agent 0.10Antifoaming agent 0.03 Disintegrating agent 0.20 Stabilizer 0.05 Filler0.13 Total 100.00

[0033] Acephate 97.5% granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

Example 4

[0034] Acephate 90% Granules can be prepared as follows:

[0035] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 91.38 Dispersing agent 00.75 Wetting agent 00.10 Binding agent00.20 Antifoaming agent 00.03 Disintegrating agent 01.00 Stabilizer00.50 Filler 06.04 Total 100.00

[0036] Acephate 90% granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

EXAMPLE 5

[0037] Acephate 85% granules can be prepared as follows:

[0038] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 86.30 Dispersing agent 01.50 Wetting agent 00.50 Binding agent01.00 Antifoamer 00.05 Disintegrating agent 02.00 Stabilizer 00.60Filler 08.05 Total 100.00

[0039] Acephate 85% granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

Example 6

[0040] Acephate 75% Granules can be prepared as follows:

[0041] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 76.15 Dispersing agent 2.00 Wetting agent 1.50 Binding agent 1.50Antifoaming agent 0.06 Disintegrating agent 5.00 Stabilizer 0.75 Filler13.04 Total 100.00

[0042] Acephate 75% Granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

Example 7

[0043] Acephate 50% Granules can be prepared as follows:

[0044] Composition Ingredients Quantity (% w/w) Acephate Technical 98.5%purity 50.77 Dispersing agent 3.00 Wetting agent 2.00 Binding agent 3.00Antifoaming agent 0.08 Disintegrating agent 10.00 Stabilizer 1.00 Filler30.15 Total 100.00

[0045] Acephate 50% Granules with above composition can be prepared byfollowing the process described in EXAMPLE 1.

Example 8

[0046] Acephate 40% granules can be prepared as follows:

[0047] Composition Ingredient Quantity (% w/w) Acephate Technical 98.5%purity 40.61 Dispersing agent 4.50 Wetting agent 3.00 Binding agent 3.00Antifoaming agent 0.08 Disintegrating agent 12.00 Stabilizer 1.50 Filler35.31 Total 100.00

[0048] Acephate 40% Granules of above composition can be prepared byfollowing the process described in EXAMPLE 1.

Tests

[0049] The physical properties of Acephate granules were determinedbefore and after aging at 45° C. for 500 hrs and for flowability,wetting time, attrition test, disintegration rate, tap density,suspensibility, sedimentation and persistent foam. No noticeabledifference in all the above properties was observed. The dynamic wettingtime and solubility test was measured as per MT-167 of CIPAC. Theflowability was measured as per MT-172 of CIPAC. The dry sieve analysiswas measured as per MT-170 of CIPAC. The sedimentation was measured asper MT-15.1 of CIPAC. Dustiness of granules was measured as per MT-171of CIPAC. The tap density was measured as per MT-58.4 and MT-33 ofCIPAC. The Acephate technical was determined by the GLC method publishedin AOAC.

[0050] Although the present invention has been disclosed in terms of apreferred embodiment, it will be understood that numerous additionalmodifications and variations can be made without departing from thescope of the invention as defined by the following claims.

What is claimed is:
 1. A process for preparing soluble granulescomprising a) premixing 40 to 98 wt. % an insecticidally active compoundof the following formula:

wherein R and R¹ individually are an alkyl, alkenyl or alkynyl groupcontaining up to 6 carbon atoms, R² is hydrogen, an alkyl groupcontaining 1 to 18 carbon atoms, a cycloalkyl group containing 3 to 8carbon atoms, an alkenyl group containing 2 to 18 carbon atoms or analkynyl group containing 3 to 18 carbon atoms, R³ is hydrogen or analkyl group containing 1 to 6 carbon atoms, and Y is oxygen or sulfur;0.1-5.0 wt. % a dispersing agent; 0.1-3.0 wt. % a wetting agent; 0.1-3.0wt. % a binding agent; 0.01-0.08 wt. % an antifoaming agent; 0.01-10.0wt. % a disintegrating agent; 0.01-1.0 wt. % a stabilizer; and fillersto make 100 wt. %, to form a premix comprising essentially 95-99% solidsand 1-5% moisture and/or solids; b) grinding said premix to produce aground product having a predetermined particle size; c) post-mixing saidground product to produce a mixture; d) granulating said mixture toproduce granules; e) drying said granules to produce dry granules; f)sizing said dry granules to produce sized granules having apredetermined length and a predetermined diameter; and g) sieving saidsized granules to separate fines which are less than said predeterminedlength and said predetermined diameter.
 2. The process of claim 1,wherein said ground product has a predetermined particle size of 5-10microns.
 3. The process of claim 1, wherein said dry granules have apredetermined length of 1.5-3.0 mm.
 4. The process of claim 1, whereinsaid dry granules have a predetermined diameter of 0.5 to 1.0 mm.
 5. Theprocess claimed in claim 1, wherein said fillers are solids in powderform.
 6. The process of claim 1, wherein said binding agent is a blendof sucrose and starch derivatives.
 7. The process of claim 1, whereinsaid wetting agent is selected from the group comprising calcium salt ofalkyl aryl sulphonate and sodium salt of alkyl aryl sulphonate.
 8. Theprocess of claim 1, wherein said dispersing agent is a derivative ofsulfonated fatty alcohol.
 9. The process of claim 1, wherein saiddisintegrating agent is a swelling type clay selected from the groupcomprising bentonite and zeolite.
 10. The process of claim 1, whereinsaid antifoaming agent is silicon oil derivative.
 11. The process ofclaim 1, wherein said stabilizer is a salt of a higher fatty acid. 12.The process of claim 1, wherein said fillers are selected from the groupcomprising precipitated silica and kaoline.
 13. The process of claim 1,wherein said granulation is accomplished by passing said mixture throughan orifice having and inlet and an outlet.
 14. The process of claim 13,wherein said inlet has a temperature of 30-35° C.
 15. The process ofclaim 13, wherein said outlet has a temperature of 40-45° C.
 16. Theprocess of claim 1, wherein said drying is accomplished by passing saidgranules though an air chamber.
 17. The process of claim 1, wherein saidgrinding is accomplished by a microniser.
 18. The process of claim 1,wherein said sizing is accomplished by an oscillating cutter.
 19. Theprocess of claim 1, wherein said insecticidally active compound isacephate.
 20. The process of claim 1, further comprising; h) recyclingsaid fines into step d).
 21. The process of claim 20, wherein saidinsecticidally active compound is acephate.
 22. The process of claim 21,wherein said ground product has a predetermined particle size of 5-10microns.
 23. The process of claim 22, wherein said dry granules have apredetermined length of 1.5-3.0 mm and a predetermined diameter of 0.5to 1.0 mm.
 24. The process of claim 23, wherein said binding agent is ablend of sucrose and starch derivatives.
 25. The process of claim 24,wherein said wetting agent is selected from the group comprising calciumsalt of alkyl aryl sulphonate and sodium salt of alkyl aryl sulphonate.26. The process of claim 25, wherein said dispersing agent is aderivative of sulfonated fatty alcohol.
 27. The process of claim 26,wherein said disintegrating agent is a swelling type clay selected fromthe group comprising bentonite and zeolite.
 28. The process of claim 27,wherein said antifoaming agent is silicon oil derivative.
 29. Theprocess of claim 28, wherein said stabilizer is a salt of a higher fattyacid.
 30. The process of claim 29, wherein said fillers are selectedfrom the group comprising precipitated silica and kaoline.
 31. Theprocess of claim 20, wherein said granulation is accomplished by passingsaid mixture through an orifice having and inlet and an outlet.
 32. Theprocess of claim 31, wherein said inlet has a temperature of 30-35° C.and said outlet has a temperature of 40-45° C.
 33. The process of claim32, wherein said drying is accomplished by passing said granules thoughan air chamber.
 34. The process of claim 33, wherein said grinding isaccomplished by a microniser.
 35. The process of claim 34, wherein saidsizing is accomplished by an oscillating cutter.